Hi all,
I'm doing lattice constant optimization for monoclinic unit cell (ibrav) of CuO. During the calculation I found that the "a vector" doesn't seem to be fixed like (a, 0, 0) along x-axis direction. It rotates a little along y-axis. Here is one example of the CELL_PARAMETER in the output: --------------- CELL_PARAMETERS (alat= 8.59525235) 1.000026260 0.001522869 0.000000000 -0.161678076 1.130837816 0.000000000 0.000000000 0.000000000 0.836873694 --------------- Here you can see that a vector = (1.000026260 0.001522869 0.000000000), not like (a, 0, 0). I never had this problem in the past when I was doing vc-relax for other cubic (ibrav = 1), hexagonal (ibrav = 4) and rhombohedral (ibrav = 5) systems. I even tried to fix all the coordinates of the Cu and O atoms to see how the lattice vectors would change. But it still made the a vector rotate to y-axis a little. Do you think it's because there is something wrong in my vc-relax input? I also pasted my input below for you to look at. Thank you, Xu Huang Department of Chemistry, University of Iowa &CONTROL calculation = 'vc-relax', pseudo_dir = '/import/u/u1/uaf/uaxhuang1/pwf/', prefix = 'CuO', outdir = './temp/', etot_conv_thr = 1.0D-5, forc_conv_thr = 1.0D-4, ! restart_mode = 'restart', / &system ibrav = 12, celldm(1) = 8.595680686, celldm(2) = 1.142694843, celldm(3) = 0.837058209, celldm(4) = -0.140538276, nat = 8, ntyp = 3, ecutwfc = 35, ecutrho = 280, occupations = 'smearing', smearing = 'mv', degauss = 0.02, nspin = 2, starting_magnetization(1) = 0.1, starting_magnetization(2) = -0.1, lda_plus_u = .true., Hubbard_U(1) = 1.0d-10, Hubbard_U(2) = 1.0d-10, / &electrons electron_maxstep = 100, mixing_beta = 0.2, conv_thr = 1.0d-7, / &ions / &CELL press = 0.0, / ATOMIC_SPECIES Cu1 1.0 Cu.pbe-d-rrkjus.UPF Cu2 1.0 Cu.pbe-d-rrkjus.UPF O 1.0 O.pbe-rrkjus.UPF ATOMIC_POSITIONS (crystal) Cu2 0.250000000 0.000000000 0.250000000 Cu1 0.750000000 0.500000000 0.250000000 Cu1 0.750000000 0.000000000 0.750000000 Cu2 0.250000000 0.500000000 0.750000000 O 0.000000000 0.250000000 0.440456316 O 0.500000000 0.250000000 0.940456316 O 0.000000000 0.750000000 0.559543684 O 0.500000000 0.750000000 0.059543684 K_POINTS (automatic) 6 6 6 1 1 1
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